The present invention relates to the field of contact lens cleaning and disinfecting. In particular, this invention relates to liquid enzyme compositions and methods for cleaning human-worn contact lenses with those compositions. The invention also relates to methods of simultaneously cleaning and disinfecting contact lenses by combining the liquid enzyme compositions of the present invention with a chemical disinfecting agent.
Various compositions and methods for cleaning contact lenses have been described in the patent and scientific literature. Some of these methods have employed compositions containing surfactants or enzymes to facilitate the cleaning of lenses. The first discussion of the use of proteolytic enzymes to clean contact lenses was in an article by Lo, et al. in the Journal of The American Optometric Association, volume 40, pages 1106-1109 (1969). Methods of removing protein deposits from contact lenses by means of proteolytic enzymes have been described in many publications since the initial article by Lo, et al., including U.S. Pat. No. 3,910,296 (Karageozian, et al.).
Numerous compositions and methods for disinfecting contact lenses have also been described. Those methods may be generally characterized as involving the use of heat and/or chemical agents. Representative chemical agents for this purpose include organic antimicrobials such as benzalkonium chloride and chlorhexidine, and inorganic antimicrobials such as hydrogen peroxide and peroxide-generating compounds. U.S. Pat. Nos. 4,407,791 and 4,525,346 (Stark) describe the use of polymeric quaternary ammonium compounds to disinfect contact lenses and to preserve contact lens care products. U.S. Pat. Nos. 4,758,595 and 4,836,986 (Ogunbiyi) describe the use of polymeric biguanides for the same purpose.
Various methods for cleaning and disinfecting contact lenses at the same time have been proposed. Such methods are described in U.S. Pat. Nos. 3,873,696 (Randeri, et al.) and 4,414,127 (Fu), for example. A representative method of simultaneously cleaning and disinfecting contact lenses involving the use of proteolytic enzymes to remove protein deposits and a chemical disinfectant (monomeric quaternary ammonium compounds) is described in Japanese Patent Publication 57-24526 (Boghosian, et al.). The combined use of a biguanide (i.e., chlorhexidine) and enzymes to simultaneously dean and disinfect contact lenses is described in Canadian Patent No. 1,150,907 (Ludwig). Methods involving the combined use of dissolved proteolytic enzymes to clean and heat to disinfect are described in U.S. Pat. No. 4,614,549 (Ogunbiyi). The combined use of proteolytic enzymes and polymeric biguanides or polymeric quaternary ammonium compounds is described in copending, and commonly assigned U.S. patent application Ser. No. 08/156,043 and in corresponding European Patent Application Publication No. 0 456 467 A2.
The commercial viability of prior enzyme/disinfectant combinations has depended on the use of a stable enzyme tablet. More specifically, the use of solid enzymatic cleaning compositions has been necessary to ensure stability of the enzymes prior to use. In order to use such compositions, a separate packet containing a tablet must be opened, the tablet must be placed in a separate vial containing a solution, and the tablet must be dissolved in order to release the enzyme into the solution. This practice is usually performed only once a week due to the cumbersome and tedious procedure and potential for irritation and toxicity. Moreover, the enzymatic cleaning tablets contain a large amount of excipients, such as effervescent agents (e.g., bicarbonate) and bulking agents (e.g., compressible sugar). As explained below, such excipients can adversely affect both cleaning and disinfection of the contact lenses.
There have been prior attempts to use liquid enzyme compositions to clean contact lenses. However, those attempts have been hampered by the fact that aqueous liquid enzyme compositions are inherently unstable. When a proteolytic enzyme is placed in an aqueous solution for an extended period (i.e., several months or more), the enzyme may lose all or a substantial portion of its proteolytic activity. Steps can be taken to stabilize the compositions, but the use of stabilizing agents may have an adverse effect on the activity of the enzyme. For example, stabilizing agents can protect enzymes from chemical instability problems during storage in an aqueous liquid, by placing the enzymes in a dormant physical conformation. This conformation is referred to herein as being "partially denatured." However, such agents may also inhibit the ability of the enzymes to become active again (i.e., become "renatured") at the time of use. Finally, in addition to the general problems referred to above, a commercially viable liquid enzyme preparation for treating contact lenses must be relatively nontoxic, and must be compatible with other chemical agents used in treating contact lenses, particularly antimicrobial agents utilized to disinfect the lenses.
The following patents may be referred to for further background concerning prior attempts to stabilize liquid enzyme formulations: U.S. Pat. Nos. 4,462,922 (Boskamp); 4,537,706 (Severson); and 5,089,163 (Aronson). These patents describe detergent compositions containing enzymes. The detergent compositions may be used to treat laundry, as well as other industrial uses. Such detergents are not appropriate for treating contact lenses. The compositions of the present invention do not contain a detergent, or other agents potentially damaging or irritating to the eye.
U.S. Pat. No. 5,281,277 (Nakagawa) and Japanese Kokai Patent Applications Nos. 92-370197; 92-143718; and 92-24325 describe liquid enzyme compositions for treating contact lenses. The compositions of the present invention are believed to provide significant improvements relative to the compositions described in those publications.